CT (computed tomography scanning) apparatus, MRI apparatus and the like are generally known as apparatus for imaging the shape of the brain.
A CT apparatus is an apparatus that uses the method of computed tomographic imaging: a device for outputting x-ray radiation rotates around a living body and irradiates it from multiple directions, and a computer performs calculations on the detected data to create images.
An MRI apparatus is an apparatus that uses the method of magnetic resonance imaging: the spin of atomic nuclei of the body tissue of a subject placed in a static magnetic field is excited by high wavelength signals for the particular Larmor frequency for those nuclei, and images are created from magnetic resonance signals that are given off accompanying this excitation.
Each of these apparatus—CT and MRI—has been developed with the goal of detecting brain structure, brain lesions, and the like.
Because the CT apparatus can clearly distinguish between the skull and the brain matter, it is used for preoperative examination before brain surgery. It is also capable of rendering blood vessels as small as 1 mm.
However, because of the exposure to radiation accompanying the CT apparatus use, with rare exceptions, CT is not performed on healthy persons as a rule, and it is only selected as a last option and used when there is a suspicion of illness. For example, a CT scan of the lungs might be performed in a regularly scheduled physical examination, but this would be to find a small tumor in the lungs, or the like. In this way, the use of CT apparatus is restricted in brain structural imaging because of radiation exposure. In addition, although images can be obtained distinguishing the cortex and the white matter of the brain, they have not been as clear as could be desired.
With the MRI apparatus, on the other hand, there are no constraints on its use in brain structural imaging because there is no fear of radiation exposure, and images can be obtained as easily and freely as photographs of the brain. Currently, because it can even detect brain lesions of around 1 mm, it is used even in regularly scheduled physical examinations. Three-dimensional (3D) MRI is also commonly used, and it has become possible to investigate the structure of the brain in detail by reconstructing it from any angle.
In addition, the MRI apparatus does an excellent job of visualizing the brain structure at the corticomedullary junction, which divides the cortex and the white matter.
Five types of imaging methods are normally used in brain MRI: T1-weighted imaging, proton-weighted imaging, T2-weighted imaging, FLAIR imaging and diffusion-weighted imaging.
In T1-weighted images, the white matter is rendered in white, and the cortex, in gray. Lesions are mainly rendered in shades of black.
In proton-weighted images, T2-weighted images and FLAIR (Fluid Attenuated Inversion Recovery) images, the white matter is, conversely, rendered in black, and the cortex, in gray. Lesions are mainly rendered in white.
In diffusion-weighted images, the cortex and white matter are rendered uniformly in gray, and lesions are rendered in white. As an example of technology concerning conventional MRI apparatus, Patent Reference 1 proposes a magnetic resonance imaging method and apparatus in which, in a magnetic resonance imaging method wherein a subject body placed in a static magnetic field is subjected first to an inversion sequence including inversion pulses, and after the inversion sequence, to an imaging sequence for collecting magnetic resonance signals from the subject body, the frequency band width of the inversion pulses is set wider than previously used bandwidths.
This magnetic resonance imaging method and apparatus makes it possible, in magnetic resonance imaging using an IR series sequence including inversion pulses, to perform imaging that actively utilizes the phenomena of chemical exchange and/or cross relaxation among a pool of a plurality of kinds of atomic nuclei; and it is stated, for example, that contrast is improved between white matter and gray matter and the like, and that the S/N ratio is improved, thus improving, for example, its ability to render brain neural tissue, and making it possible to obtain MRI images of previously unobtainable high quality. (This technology will be referred to below as Previous Example 1.)
In addition, Patent Reference 2 proposes a magnetic resonance imaging apparatus in which, in a magnetic resonance imaging apparatus provided with an acquisition means, whereby a nuclear magnetic resonance signal is generated at the subject body under specified conditions of image acquisition and then detected, a reconstruction means for reconstructing tomographic images of the subject body based on nuclear magnetic resonance signals, a display means for displaying tomographic images of the subject body, and a control means for controlling the image acquisition means, the reconstruction means and the display means; the control means continuously displays at least 2 types of contrast images on the same screen or on a plurality of screens. For the plurality of types of contrast images, 2 types of contrast images, such as a proton density-weighted image and a T2-weighted image, a T1-weighted image and a T2-weighted image, or a fat-water synthetic image and a fat-suppressed image can be selected according to the lesion being targeted.
This magnetic resonance imaging apparatus is said to make it possible to advance a puncture needle, biopsy needle or the like to a lesion site in a subject body with an image corresponding to the lesion and rendered with higher contrast as a guide. (This technology will be referred to below as Previous Example 2.)    Patent Reference 1: Tokkai [Japan unexamined patent application publication] no. H9-253067    Patent Reference 2: Tokkai no. 2001-70285